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Session 71 - Globular Clusters.
Display session, Wednesday, January 15
Metropolitan Ballroom,

[71.07] Cool Stars in the Halo

J. E. Gizis (Caltech)

We present observations of the coolest stars in the Galactic Halo, the M-subdwarfs. A new spectroscopic classification system for M-dwarfs and M-subdwarfs is based upon quantitative measures of TiO and CaH features in the region \lambda\lambda 6200 - 7400 ÅUsing synthetic spectra computed by Allard and Hauschildt (1995), we derive metallicities for the stars. Stars are classified as dwarfs (M V), subdwarfs (sdM), or extreme subdwarfs (esdM). These classifications correspond to [m/H] \approx 0.0, -1.2, and -2.0 respectively. Our metallicity scale agrees with theoretical HR diagrams and HST globular cluster measurements. We discuss some nearby subdwarfs of particular interest in light of our metallicity scale. We also present a preliminary luminosity function for the low-mass stars in the halo based on a new proper motion survey.

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